scholarly journals Alternating lysis and lysogeny is a winning strategy in bacteriophages due to Parrondo’s Paradox

2021 ◽  
Author(s):  
Kang Hao Cheong ◽  
Tao Wen ◽  
Sean Benler ◽  
Eugene V. Koonin
Keyword(s):  
Game Theory ◽  
Population Density ◽  
Winning Strategy ◽  
Host Population ◽  
Host Cells ◽  
Dynamic Evolution ◽  
Reproduction Rate ◽  
Host Parasite Interactions ◽  
Parrondo’S Paradox ◽  
Host Parasite

AbstractTemperate bacteriophages lyse or lysogenize the host cells depending on various parameters of infection, a key one being the host population density. However, the effect of different propensities of phages for lysis and lysogeny on phage fitness is an open problem. We explore a nonlinear dynamic evolution model of competition between two phages, one of which is disadvantaged in both the lytic and lysogenic phases. We show that the disadvantaged phage can win the competition by alternating between the lytic and lysogenic phases, each of which individually is a “loser”. This counter-intuitive result recapitulates Parrondo’s paradox in game theory, whereby individually losing strategies can combine to produce a winning outcome. The results suggest that evolution of phages optimizes the ratio between the lysis and lysogeny propensities rather than the phage reproduction rate in any individual phase. These findings are expected to broadly apply to the evolution of host-parasite interactions.

scholarly journals Fluctuations in population densities inform stability mechanisms in host-parasitoid interactions

2021 ◽  
Author(s):  
Abhyudai Singh
Keyword(s):  
Population Dynamics ◽  
Population Density ◽  
Functional Response ◽  
Discrete Time ◽  
Host Population ◽  
Reproduction Rate ◽  
Population Densities ◽  
Type Iii ◽  
Time Formalism ◽  
Large Fluctuations

AbstractPopulation dynamics of host-parasitoid interactions has been traditionally studied using a discrete-time formalism starting from the classical work of Nicholson and Bailey. It is well known that differences in parasitism risk among individual hosts can stabilize the otherwise unstable equilibrium of the Nicholson-Bailey model. Here, we consider a stochastic formulation of these discrete-time models, where the host reproduction is a random variable that varies from year to year and drives fluctuations in population densities. Interestingly, our analysis reveals that there exists an optimal level of heterogeneity in parasitism risk that minimizes the extent of fluctuations in the host population density. Intuitively, low variation in parasitism risk drives large fluctuations in the host population density as the system is on the edge of stability. In contrast, high variation in parasitism risk makes the host equilibrium sensitive to the host reproduction rate, also leading to large fluctuations in the population density. Further results show that the correlation between the adult host and parasitoid densities is high for the same year, and gradually decays to zero as one considers cross-species correlations across different years. We next consider an alternative mechanism of stabilizing host-parasitoid population dynamics based on a Type III functional response, where the parasitoid attack rate accelerates with increasing host density. Intriguingly, this nonlinear functional response makes qualitatively different correlation signatures than those seen with heterogeneity in parasitism risk. In particular, a Type III functional response leads to uncorrelated adult and parasitoid densities in the same year, but high cross-species correlation across successive years. In summary, these results argue that the cross-correlation function between population densities contains signatures for uncovering mechanisms that stabilize consumer-resource population dynamics.

scholarly journals Hidden paths to endless forms most wonderful: Parasite-blind diversification of host quality

2020 ◽  
Author(s):  
Lisa Freund ◽  
Marie Vasse ◽  
Gregory J. Velicer
Keyword(s):  
Growth Suppression ◽  
Host Population ◽  
Host Quality ◽  
Evolution Theory ◽  
Evolutionary Diversification ◽  
Adaptive Landscapes ◽  
Host Parasite Interactions ◽  
Parasite Evolution ◽  
Host Parasite ◽  
Selective Environment

Evolutionary diversification can occur in allopatry or sympatry, can be unselected or driven by selection, and can be phenotypically manifested immediately or remain phenotypically latent until later manifestation in a newly encountered environment. Diversification of host-parasite interactions is frequently studied in the context of intrinsically selective coevolution, but the potential for host-parasite interaction phenotypes to diversify latently during parasite-blind evolution is rarely considered. Here we use a social bacterium experimentally adapted to several environments in the absence of phage to analyse allopatric diversification of latent host quality - the degree to which a host population supports a viral epidemic. Phage-blind evolution reduced host quality overall, with some bacteria becoming completely resistant to growth suppression by phage. Selective-environment differences generated only mild divergence in host-quality. However, selective environments nonetheless played a major role in shaping evolution by determining the degree of stochastic diversification among replicate populations within treatments. Ancestral motility genotype was also found to strongly shape patterns of latent hostquality evolution and diversification. These outcomes show that adaptive landscapes can differ in how they constrain stochastic diversification of a latent phenotype and that major effects of selection on biological diversification can be missed by focusing on trait means. Collectively, our findings suggest that latent-phenotype evolution (LPE) should inform host-parasite evolution theory and that diversification should be conceived broadly to include latent phenotypes.

scholarly journals Critical aspects of phytoalexins in potato

1987 ◽  
Vol 59 (3) ◽  
pp. 217-230
Author(s):  
Sture Brishammer
Keyword(s):  
Host Cells ◽  
Potato Tubers ◽  
Inhibitory Effects ◽  
Host Parasite Interactions ◽  
Different Types ◽  
Endogenous Elicitor ◽  
Artificial Inoculations ◽  
Host Parasite ◽  
Critical Aspects

Phytoalexins in potato are sesquiterpenoid substances produced in response to infections and are believed to help plants resist attack by pathogens. However, these compounds appear in response to compatible as well as incompatible interactions and only accumulate in the tubers. The amounts of phytoalexins produced depend on the physiological condition of the tubers. Young tubers don’t get easily infected with Phytophthora infestans even though they synthesize extremely small amounts of phytoalexins. Furthermore, confusion as to the identity of specific races and the propensity for a given race to produce different effects in the same type of host makes it extremely difficult to predict host-parasite interactions with any acceptable degree of accuracy. It is doubtful that the production of phytoalexins in response to artificial inoculations is representative of that occurring in natural infections. Markedly different types of pathogens induce synthesis of same substances in the host cells. It therefore seems most probable that all the phytoalexins are synthesized in response to stimulation by an endogenous elicitor. Little knowledge is available regarding the biosynthesis of these sesquiterpenes, and many previous determinations have presumably been erroneous. When potato tubers were inoculated with the late blight fungus, secondarily appearing bacteria were not retarded, despite the presence of phytoalexins. There is no generally accepted hypothesis describing the mechanism by which phytoalexins inhibit pathogens and no distinction has been made between the effects on necrotrophs and biotrophs. Adequate bioassays capable of measuring the effects of inhibition have yet to be developed, thus far, no convincing inhibitory effects have been reported. During purification of the phytoalexins there is a high risk for artifact forming, implying that specific compounds cannot be detected with certainty. Moreover, present analytical methods must be improved before we can determine how phytoalexins act in vivo. Probably, phytoalexins are synthesized at a stage in the infection too late to be able to restrict its expansion with the tissues of the host. Phytoalexins are restricted to the attacked parts of the tubers and there is no evidence indicating that these compounds pose any health risks when present in potatoes used for consumption.

Population interactions between a parasitic castrator, Probopyrus pandalicola (Isopoda: Bopyridae), and one of its freshwater shrimp hosts, Palaemonetes paludosus (Decapoda: Caridea)

Parasitology ◽  
1979 ◽  
Vol 79 (3) ◽  
pp. 431-449 ◽  
Author(s):  
J. T. Beck
Keyword(s):  
Host Population ◽  
Acartia Tonsa ◽  
Parasite Control ◽  
Freshwater Shrimp ◽  
Free Swimming ◽  
Host Parasite Interactions ◽  
Population Interactions ◽  
Parasitic Castrator ◽  
Host Parasite ◽  
And Control

SUMMARYFreshwater shrimp, Palaemonetes paludosus, infected by the bopyrid isopod, Probopyrus pandalicola, occurred as far as 33 km upstream in many coastal rivers and canals throughout Florida. Free-swimming isopod larvae and the intermediate copepod host, Acartia tonsa, were collected in the plankton of the Wakulla River, and it appeared that cryptoniscus larvae swam at least as far as 13 km upstream to infect the definitive shrimp host after leaving the copepod in brackish water. In the Wakulla River infection levels ranged from 87·5 to 100%. In contrast, at McBride's Slough infection levels fluctuated from 0·9 to 93·2%. In the St Marks River the frequency of infected shrimp gradually increased from 0% upstream to 96%, 6 km further downstream. A significantly greater percentage of female than male hosts were infected, but only females of size classes less than 31 mm long had a greater frequency of infection. Female P. pandalicola were greatly under-dispersed (coefficient of dispersion (s2/x¯) less than 1) throughout the host population; 99·6% of the infected hosts carried only 1 female parasite. Control of P. pandalicola at the infrapopulation level is probably accomplished by some mode of intraspecific competition, and control at the suprapopulation level occurs through an upstream limitation of the transmission range of the cryptoniscus larval stage. Host–parasite interactions appear to be unstable.

scholarly journals Expanding the antimalarial toolkit: Targeting host–parasite interactions

2016 ◽  
Vol 213 (2) ◽  
pp. 143-153 ◽  
Author(s):  
Jean Langhorne ◽  
Patrick E. Duffy
Keyword(s):  
First Generation ◽  
Host Cells ◽  
Mammalian Host ◽  
Drug Resistant ◽  
Intracellular Growth ◽  
Partial Protection ◽  
Anopheles Mosquitoes ◽  
Host Parasite Interactions ◽  
New Research ◽  
Host Parasite

Recent successes in malaria control are threatened by drug-resistant Plasmodium parasites and insecticide-resistant Anopheles mosquitoes, and first generation vaccines offer only partial protection. New research approaches have highlighted host as well as parasite molecules or pathways that could be targeted for interventions. In this study, we discuss host–parasite interactions at the different stages of the Plasmodium life cycle within the mammalian host and the potential for therapeutics that prevent parasite migration, invasion, intracellular growth, or egress from host cells, as well as parasite-induced pathology.

scholarly journals To delay once or twice: the effect of hypobiosis and free-living stages on the stability of host–parasite interactions

2008 ◽  
Vol 5 (25) ◽  
pp. 919-928 ◽  
Author(s):  
Sabrina Gaba ◽  
Sébastien Gourbière
Keyword(s):  
Population Dynamics ◽  
Life Cycle ◽  
Time Delay ◽  
Host Population ◽  
Previous Attempt ◽  
Maximal Effect ◽  
Parasite Life Cycle ◽  
Free Living ◽  
Host Parasite Interactions ◽  
Host Parasite

The life cycle of many endoparasites can be delayed by free-living infective stages and a developmental arrestment in the host referred to as hypobiosis. We investigated the effects of hypobiosis and its interaction with delay in the free-living stages on host–parasite population dynamics by expanding a previous attempt by Dobson & Hudson. When the parasite life cycle does not include free-living stages, hypobiosis destabilizes the host–parasite interactions, irrespective of the assumptions about the regulation of the host population dynamics. Interestingly, the destabilizing effect varies in a nonlinear way with the duration of hypobiosis, the maximal effect being expected for three to five months delay. When the parasite life cycle involves free-living stages, hypobiosis of short or intermediate duration increases the destabilizing effect of the first time delay. However, hypobiosis of a duration of five months or more can stabilize interactions, irrespective of the regulation of the host population dynamics. Overall, we confirmed that hypobiosis is an unusual time delay as it can stabilize a two-way interaction. Contrary to the previous conclusions, such an atypical effect does not require self-regulation of the host population, but instead depends on the existence of free-living stages.

In vivo response of Mesocestoides vogae to human insulin

Parasitology ◽  
2008 ◽  
Vol 136 (2) ◽  
pp. 203-209 ◽  
Author(s):  
L. CANCLINI ◽  
A. ESTEVES
Keyword(s):  
Human Insulin ◽  
Insulin Signalling ◽  
Reproduction Rate ◽  
Glucose Content ◽  
Parasitic Helminths ◽  
Host Parasite Interactions ◽  
Host Parasite ◽  
Different Levels ◽  
Mesocestoides Vogae

SUMMARYSuccessful host invasion by parasitic helminths involves detection and appropriate response to a range of host-derived signals. Insulin signal response pathways are ancient and highly-conserved throughout the metazoans. However, very little is known about helminth insulin signalling and the potential role it may play in host-parasite interactions. The response of Mesocestoides vogae (Cestoda: Cyclophyllidea) larvae to human insulin was investigated, focusing on tyrosine-phosphorylation status, glucose content, survival and asexual reproduction rate. Parasite larvae were challenged with different levels of insulin for variable periods. The parameters tested were influenced by human insulin, and suggested a host-parasite molecular dialogue.†

Global stability and Hopf bifurcation of a host–parasite system

2017 ◽  
Vol 10 (04) ◽  
pp. 1750047
Author(s):  
Xuerui Wei ◽  
Zhipeng Qiu
Keyword(s):  
Hopf Bifurcation ◽  
Time Scale ◽  
Sufficient Conditions ◽  
Host Population ◽  
Complete Analysis ◽  
Logistic Growth ◽  
Free Living ◽  
Dynamical Mechanism ◽  
Host Parasite Interactions ◽  
Host Parasite

Understanding the dynamical mechanism of the host–parasite interactions is one of important issues on host–parasite association. In this paper, we formulate a three-dimensional host–macroparasite system to describe the host–parasite interactions, which includes the logistic growth rate of host population, the important free-living stage and the host fecundity reduction due to parasite infection. The purpose of the paper is to investigate the asymptotical behavior of the system. By using the properties of the solution to non-autonomous linear system, the basic production number [Formula: see text] is proved to be a threshold which determines the outcome of the parasites. If [Formula: see text], the parasite will eventually die out, and if [Formula: see text] the parasite will be uniformly persistent. Hopf bifurcation of the system is further studied, and sufficient conditions for the Hopf bifurcation are obtained. By using the singular perturbation techniques, the system is separated into two time scales with a faster time scale for the free-living infective particles and a slower time scale for the population dynamics of host and parasite, and then a complete analysis of the dynamics on the slow manifold is conducted. The theoretical results show that the level of aggregation of parasites within host may influence the persistence and stability of the system.

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